FepA and FhuA both actively transport iron-containing siderophores across the outer membrane of E. coli. The structure of FepA was recently solved in our lab, and native data have been collected for FhuA cocrystallized with its cognate siderophore. FepA and FhuA share less than 20% sequence identity, but show strong indications that they are structurally homologous. We propose here to collect Fe MAD data on FhuA to use as a source of phase information to aid molecular replacement and refinement of its structure, and to identify its siderophore binding site. Single-wavelength data at the Fe edge (1.74 E) on a FepA crystal carefully soaked with its cognate siderophore will be collected in order to study its substrate binding site and mechanism.